1978 replies to this topic

[25585]

That's the point. If I have to force myself to look only at objects that are not seen, it is only frustration.
So, no, I'm not interested in wasting my nights looking for the invisible.
I prefer to aim the binoculars at what I can see more easily, in the least polluted area and it is already fun. I don't have to be an astronomer. 

 

 

I fear that the Bortle scale is not very suitable for evaluating our skies well.
You talk about Bortle 7, but I think you seem to live in a less polluted and quite dark suburb (once you turn off the neighbor's lights, "Mr. Edison"). So, you just go out on the driveway to affirm whenever you prefer 10x50 to 10x42.
Ok. it is possible to assume that your retinas are less sensitive than mine, but it is also possible that the evaluation of the light pollution of your sky is a little too high. Maybe it's B6?

 

From home, with 10x42 (for example) I can't see HIP 14030 - SAO 130241 (8.7 magn). 

There are aspects such as thermal, humidity, air currents and atmospheric pressure degrading a view that affects seeing as well. In winter, even under dark skies, people have their heating on and in summer air conditioning.

[Jon Isaacs]

 

 

That's the point. If I have to force myself to look only at objects that are not seen, it is only frustration.
So, no, I'm not interested in wasting my nights looking for the invisible.
I prefer to aim the binoculars at what I can see more easily, in the least polluted area and it is already fun. I don't have to be an astronomer.

 

You are clearly not an astronomer.  Looking for objects at the edge of perception, objects that might be invisible naked eye or in a small instrument, that is how one develops their skills.  The objects that seem invisible in the beginning, they become more easily seen with time and at some point will seem so bright it is difficult to believe they were a challenge at one time.

 

Ok. it is possible to assume that your retinas are less sensitive than mine,

 

I suspect the opposite is true.  Developing one's observing skills, the connection between the eye and brain, these are critical parts of observing fainter objects.  And understanding dark adaptation, how to maximize it, these are important observing skills.  I can look at a faint galaxy in a large scope and it looks quite apparent to me. To a normal person, they see nothing.  

 

Jon

[f18dad]

Here is my first 25 vs 50mm comparative observation report.   With observations made from my suburban driveway on Thursday 9 December 2021. Skies were slightly hazy, but clear. I would put the naked eye limiting magnitude at around 4.30 based on a sighting of Kappa Cassiopeiae (4.19 mag)

 

The instrument used is a Vortex Razor 10x50 UHD. An excellent binocular, and the sharpest 10x50 in my collection. By using the same instrument with and without 25mm aperture masks to make observations, optical quality becomes a mostly neutral factor in the comparisons. The observations are essentially comparing an excellent quality 10x50mm binocular with an excellent quality 10x25 binocular. Given the advantage of masking all but the center of the objectives, it could be argued that the resulting 10x25 binocular provides a better optical quality view than the same instrument at full aperture.

 

Observations made of the 5 day 20 hour moon support this to a certain extent. A slight CA rim seen in the full aperture view was not present in the masked view. Whether this is a consequence of the reduced illumination or the better figure in the center 25% of the objectives I do not know. The views were enjoyable both with and without the masks. At the current phase, the moon is not overly bright from my perspective so masking wasn't an improvement in that regard. The non masked view showed slightly better detail, though the difference was subtle. For example, the rim structure of a small complex of craters just west of Polybius (C,F,P on chart 57 in the Rukl atlas 1st edition) was noticeably more distinct in the unmasked view. My sense from this comparison is that a less extreme mask might be a potential benefit for lunar observation, even with a top quality binocular. Aperture masks of 42mm or even 35mm might be worth trying. Aperture masks in this range might also reduce flaring on Jupiter, for example. The aperture masks did not seem to provide a noticeable benefit improving star image quality for brighter stars, which is quite good overall but somewhat dependent on eye positioning. I did not spend much time evaluating this characteristic, honestly.

 

More can be seen with a 10x25mm binocular in deep sky observing than I had anticipated.  This is not to say that differences between 25 and 50mm are not apparent. But it is understandable that the differences might not be conspicuous to an observer unfamiliar with 10x50 binoculars and possessing limited knowledge of the night sky. Overall, many more faint stars (8-9.5 magnitude range) can be seen with a mounted 10x50 binocular compared to the view with the same instrument masked to 25mm. Hand held, the magnitude limits at either aperture are reduced by say 1.5-2 magnitudes. 

 

M45 / Pleiades

 

The view with the 25mm binocular is pleasing, frankly. But comparing it directly with 50mm aperture it is obvious and undeniable that fainter stars are brighter and more readily seen. Specifics?

 

 

1. 8.77 mag Seen in direct vision at 50mm and quite difficult in averted with 25mm, seen perhaps 20% of the time.

2. 7.78 mag Seen in direct vision at 50mm but in averted at 25mm. seen perhaps 50% of the time.

3. 9.90 mag Seen in averted perhaps 25% of the time at 50mm. Not seen at 25mm.

4. STFA 8 8.26/8.72 54.7". Easily resolved in direct vision at 50mm (and quite fun). Difficult at 25mm. Primary(?) seen readily in averted. Secondary glimpsed 25% of time.

5. S 437 AB,C 8.13/7.70 38.8. Easily resolved in direct vision at 50mm (and quite fun). Somewhat challenging in averted at 25mm. Seen 75% of time.

 

M52 Open Cluster Cassiopeia

Cluster seen faintly in averted as nebulous glow with brightest star in cluster (SAO 20606 / 8.27 mag) readily seen in direct view at 50mm. Cluster not seen at 25mm. SAO 20606 occasionally glimpsed in averted.

 

WZ Cassiopeia / STTA 254

50mm: Double resolved at 50mm red and blue colors distinct. 25mm Primary seen steadily and red color discenable though not as apparent compared with 50mm view. Secondary seen in averted perhaps 50% of the time. Color not apparent. Frankly, I was impressed the secondary could be glimpsed at 25mm. Had not anticipated that. Secondary is 8.30 magnitude.

 

NGC 457 Open Cluster Cassiopeia

Phi Cas and HD 7902 (the owl's eyes) readily seen at both apertures. At 25mm the rest of the cluster appears as a faint nebulosity in averted vision. It is much brighter at 50mm with 6-8 stars resolved in averted vision and additional grainy nebulosity from partially resolved cluster members.

 

Perseus Moving Group

Perhaps 25% additional faint stars seen at 50mm compared with 25mm. 

 

Kemble's Cascade / NGC 1502 / STF 485

The cascade is faint but seen steadily in averted at 50mm. At 25mm some of the stars can be seen in averted but not the entire string. NGC 1502: a faint granularity with a few stars flickering in averted at 50mm. Not seen at 25mm. STF 485 (6.9/6.9 17.7") is slightly challenging but not hard to resolve at 50mm. It is quite difficult to resolve at 25mm. Presumably the issue is the comparatively small (for binoculars) separation. 

 

M37/M36/M38 Auriga

I was able to see all three of these clusters in averted vision at 25mm, which came as a surprise to me.  All three were more easily seen at 50mm, needless to say, and stars were resolved in both M38 and M36 at 50mm that could not be seen at 25mm, but I was nevertheless impressed that the clusters could been seen at all with such a small aperture under suburban skies.

 

STF 764 Auriga

6.38/7.08 25.6" pa 14*

A recent favorite double of mine. Readily seen and fun at both 25 and 50mm aperture.

 

Thank you for reading. 

 

Fiske. This is an awesome report. I enjoyed reading it. Thank you so much for doing it. I look forward to more. May I suggest without committing heresy here that you are the growing legacy of edZ?

 

This report is exactly what CN and especially this forum is all about.

 

I would also suggest that your retinal sensitivity is primus and your observational acuity is par excellence.

[Grimnir]

You are clearly not an astronomer.  Looking for objects at the edge of perception, objects that might be invisible naked eye or in a small instrument, that is how one develops their skills.  The objects that seem invisible in the beginning, they become more easily seen with time and at some point will seem so bright it is difficult to believe they were a challenge at one time.

 

I suspect the opposite is true.  Developing one's observing skills, the connection between the eye and brain, these are critical parts of observing fainter objects.  And understanding dark adaptation, how to maximize it, these are important observing skills.  I can look at a faint galaxy in a large scope and it looks quite apparent to me. To a normal person, they see nothing.  

 

Jon

 

On the money!

 

Graham

[tmichaelbanks]

Wow, great report Fiske!   

 

Proof positive that you can enjoy the night sky without huge apertures!

 

That you could see so many DSOs both with and without masking matches my much more casual experience with my Pentax 8x25.  Using it at the shore this past summer looking at dark skies out over the ocean brought a surprising number of objects into view.

[gwlee]

I have also been impressed by how much I can see in the night sky through my 8x32 EL, but of course I can see more, more, and more stars through my 8x42, 7x50, and 10x50.

[gwlee]

I believe a person that’s interested optical theory and principles, but has little or no interest in learning to become an observer will find it more difficult to plumb the depths of optical theory than an observer with equal interest in optics. 

[KennyJ]

Very interesting observing report, Fiske ( as always ).

 

I trust neither the author Fiske nor any other readers consider it impertinent of me to state the obvious, yet strangely omitted factor involved here, apart from aperture v aperture per se.

 

That is of course, the greatly increased focal ratio induced by the aperture reduction with all else unchanged.

 

This in itself will serve to render some stars and separations "doable" that would otherwise not necessarily be so at the shorter focal ratio.

 

Kenny

[Fiske]

Thanks everyone for your kind remarks. I'm happy the report has been well received. It's flattering but a considerable stretch IMO to compare my contributions with those of edZ, the volume of whose posts and the rigorous detail of whose reviews is unparalleled. Not to mention the many current contributors with far more experience in astronomy and knowledge of optics than I possess. I feel fortunate to have the benefit of their opinions and wisdom

 

I look forward to making 25 vs 50mm aperture observations from a darker site. 

[Fiske]

Henry, in regard to your question concerning NGC 1981 in Orion, about the difference between a 25 versus 50mm aperture view of the cluster, keep in mind that it is not in the Milky Way, and therefore not rich in fainter stars. Here is the difference I would anticipate seeing with a mounted 10x50 binocular at full aperture. Also note that this is dependent on the instrument being mounted, not handheld. Hand holding results in at least a 1.5 magnitude loss, if not more.

 

 

The faint star you indicate (HD 36842) is reported as 8.13 magnitude, which is consistent with what I observed last night with the binocular masked at 25mm aperture. Stars 1 and 2 should also be visible in the 10x50, based on their magnitudes as listed in Sky Safari.

 

1. HD 36957 -- 8.85 magnitude

2. HD 36998 -- 8.98 magnitude

 

As previously mentioned, the difference in seeing down to say 9.5 magnitude versus 8.3 is considerable but more conspicuous in rich star fields versus sparse fields. Consider this comparison of the Alpha Persei cluster (Melotte 20), which is in the Milky Way, simulating the view a 10x25 binocular (consistent with the magnitude limits I observed last night) compared with that of a 10x50 binocular. Sky Safari was used to create the charts.

 

Melotte 20 / Limiting magnitude: 8.3 / 10x25 view

 

 

 

Melotte 20 / Limiting magnitude: 9.5 / 10x50 view

 

Edited by Fiske, 10 December 2021 - 06:39 PM.

[ECP M42]

The objects that seem invisible in the beginning, they become more easily seen with time and at some point will seem so bright ...

... that I will have to use the sunglasses?        

 

Jon, I can understand your point. But you're confusing things. 

 

Developing one's observing skills, the connection between the eye and brain, these are critical parts of observing fainter objects.  And understanding dark adaptation, how to maximize it, these are important observing skills.  I can look at a faint galaxy in a large scope and it looks quite apparent to me. To a normal person, they see nothing. 

You are insinuating the misconception that experience and knowledge of the sky increases retinal sensitivity. But it's not true.

Seeing faint celestial objects that others don't see (assuming they have the same retinal sensitivity as you) is a property of memory, not the retina. Your brain is used to seeing those objects, it already knows them and therefore recognizes them more easily.

Habit could (perhaps) help improve sensitivity to dim lights over the years, but eye sensitivity is essentially an individual trait. That is, if you are born with a low sensitivity, you will hardly die as sensitive as an Owl. 

Edited by ECP M42, 10 December 2021 - 11:18 PM.

[ECP M42]

Hi Fiske, I was pleased to read in your report that you were surprised at the views in 10x25. This is a good sign for your retinas. 

 

 

And doing some math with your data, it appears that the 25mm light loss is rated by your eyes as less than theoretical. Or vice versa, that the gain of 50 on the 25mm is not 400%, but only 300%.
On this point we should reflect ... 

Another point is that your sky appears to be less polluted than mine. I don't know how much, but maybe even two magnitudes.

 

I look forward to making 25 vs 50mm aperture observations from a darker site. 

You will certainly see more stars with the 10x50, but it could be just as interesting.
I will gladly read. 

[Fiske]

Very interesting observing report, Fiske ( as always ).

 

I trust neither the author Fiske nor any other readers consider it impertinent of me to state the obvious, yet strangely omitted factor involved here, apart from aperture v aperture per se.

 

That is of course, the greatly increased focal ratio induced by the aperture reduction with all else unchanged.

 

This in itself will serve to render some stars and separations "doable" that would otherwise not necessarily be so at the shorter focal ratio.

 

Kenny

Kenny, thanks for your reply. And no, I don't consider your comment about focal ratio to be an impertinence. 

 

Keeping magnification constant while decreasing aperture does increase the focal ratio, as you say, but it isn't clear to me how relevant that fact is in the performance comparison between 10x25 versus 10x50 binoculars. The salient difference is the reduction in aperture, and the consequent reduction in exit pupil size and thus brightness. Theoretically, the larger aperture provides a resolution advantage, but at such low magnifications binoculars are nowhere near theoretical resolution limits, which is why small refractors that can operate at much higher magnifications are capable of resolving much closer double stars than can be observed with a binocular of the same aperture.

 

And at any rate, the observation of STF 485 in Camelopardalis in my report suggests that resolving closer doubles is not more doable at 10x25 than at 10x50. In fact, the opposite appears to be the case.

 

Now, what I would expect to find is that a 10x25 binocular shows fainter stars and has a resolution advantage over a 6x25 binocular, for example, due to the increase in magnification, which would be a consequence of increasing the focal ratio.

 

Fiske

Edited by Fiske, 11 December 2021 - 09:50 AM.

[Fiske]

Henry, in all candor I consider arguments about retinal sensitivity to be essentially silly. Surely there are differences in this regard between individual observers, but normal variation would never make a 10x25 binocular the visual equivalent of a 10x50.  I noted your previous comment that the view in your 10x25 binocular compared with a larger aperture instrument was too dark (my word would be dim), which suggests to me that you are coming to realize the significance of aperture for astronomical observation.

 

Also, I am in complete agreement with Jon (and others) about the importance of visual training in one's ability to resolve fine details. Neurologically, our minds are highly adaptable and pursuing any particular activity, whether it is astronomical observation, playing a musical instrument, reading, drawing, etc. physically changes are brains, enabling us to become more adept at the activity. This is a thoroughly documented neurological fact.

 

The way forward here is for you to continue reporting your observations of specific objects including the details of the instrument(s) used, as you have begun to do in this topic. In that way, other observers (including myself) can compare their own observations with yours and we can all be enlightened as a consequence. This is part of what makes astronomy fun. 

Edited by Fiske, 11 December 2021 - 11:09 AM.

[f18dad]

Also sprach Zarathustra!

[Fiske]

Also sprach Zarathustra!

  

 

(Avatar noted.)

[gwlee]

If a person had unusually sensitive retinas (super powers) enabling them to use a 10x25 to see what an average person could only see with a 10x50, I would expect them to see much more with a 10x50 because it gathers about four times as much light. If Superman employed a 10x50, would he be able to see things that most of us would need a 10x100 to see?

[Fiske]

If a person had unusually sensitive retinas (super powers) enabling them to use a 10x25 to see what an average person could only see with a 10x50, I would expect them to see much more with a 10x50 because it gathers about four times as much light. If Superman employed a 10x50, would he be able to see things that most of us would need a 10x100 to see?

Maybe a 25x100, unless the person also had super dilating pupils to complement the retinal super power...

 

[25585]

You are clearly not an astronomer.  Looking for objects at the edge of perception, objects that might be invisible naked eye or in a small instrument, that is how one develops their skills.  The objects that seem invisible in the beginning, they become more easily seen with time and at some point will seem so bright it is difficult to believe they were a challenge at one time.

 

I suspect the opposite is true.  Developing one's observing skills, the connection between the eye and brain, these are critical parts of observing fainter objects.  And understanding dark adaptation, how to maximize it, these are important observing skills.  I can look at a faint galaxy in a large scope and it looks quite apparent to me. To a normal person, they see nothing.  

 

Jon

Trained observation, knowing what is where, what its status is, & what's new is for all disciplines. Astronomers specialise in checking out the cosmos.... 

[gwlee]

Also, I am in complete agreement with Jon (and others) about the importance of visual training in one's ability to resolve fine details. Neurologically, our minds are highly adaptable and pursuing any particular activity, whether it is astronomical observation, playing a musical instrument, reading, drawing, etc. physically changes are brains, enabling us to become more adept at the activity. This is a thoroughly documented neurological fact.

 

Looking through a binocular isn’t the same as observing with a binocular. The latter is a skill that takes time and effort to learn. Students in many natural science classes, including astronomy, are often required to draw what they see and take detailed notes about what they see to develop their observing skills. By the end of these classes, diligent students are seeing and recording a great deal more than they thought possible at the beginning of the class. 

Edited by gwlee, 11 December 2021 - 05:11 PM.

[gwlee]

Now, what I would expect to find is that a 10x25 binocular shows fainter stars and has a resolution advantage over a 6x25 binocular, for example, due to the increase in magnification, which would be a consequence of increasing the focal ratio.

 

Fiske

Roy Bishop writes sections of  the “Optics and Observing” chapter of The Observer’s Handbook published by the RASC. including the “Binoculars” section. With a background in physics, it’s a fairly technical article, but still accessible to the layman, and like all of his work, well worth reading.

 

He argues that “Relative Brightness”, which is probably the most often cited figure for binocular performance is a “totally inadequate measure of binocular performance on the night sky.” Instead, he prefers the simple product of magnification and objective diameter as the figure merit for binocular performance on the night sky, which is sometimes called the Bishop Index. For example, the figure of merit for a 7x50 binocular is 350, and the figure of merit for 10x50 binocular is 500, so the relative performance of these two binoculars is the ratio of 350/500. 

 

I am not qualified to debate optical theory, so I don’t, but in testing and ranking the performance of all of my binoculars on the night sky, I find the Bishop Index comes as close as any calculation to predicting my empirical rankings and the math is easier to do in my head.  

 

Per Bishop, the ratio of 6x25 performance to 10x25 performance is 150/250, and the relative performance of my 8x32EL to Henry’s 10x25 is 256/250. The ratio of 10x25 to 10x50 is 250/500. How does your binocular observing experience compare to Bishop’s simplified mathematical model? 

Edited by gwlee, 11 December 2021 - 11:30 PM.

[ECP M42]

But how, Fiske? The main point for which all this discussion started (parallel to the theme "Team 10x"), is precisely the retinal sensitivity ... and now you come up with: "in all candor I consider arguments about retinal sensitivity to be essentially silly" 

 

     ... I laugh to keep from crying.

 

Underestimating or even neglecting the function of the retina in astronomy (and in all activities of seeing) is like neglecting the function of the sensor in photography, or the eardrum in acoustics or the fire in the kitchen. 

 

Obviously, the individual retinal sensitivity has a completely individual function. But that's exactly why nobody can question "the needs" of others. 

 

Surely there are differences in this regard between individual observers, but normal variation would never make a 10x25 binocular the visual equivalent of a 10x50. 

Yet it is not so, Fiske. As I have already explained, for my eyes and especially under my polluted skies, the difference between 10x25 and 10x50 is practically invisible. 

The "loss" (if there is or when there is) is so minimal that I don't care neither and I prefer instead to observe my polluted sky, avoiding the ugly milky haze of 10x50, using a more closed exit pupil (2.5mm vs 5mm). 

In this case, I'm sure the cause is retinal sensitivity (plus, of course, light pollution). 

 

However, it is always possible to install on 10x50 two metallic variable diaphragms, for changing the aperture from 50 to 5mm ... and so to play with this new strument. 

 

 

 

Also, I am in complete agreement with Jon (and others) about the importance of visual training ... is a thoroughly documented neurological fact.

Visual training does not increase the sensitivity of the retina. This is the point which must be refuted to Jon. 

 

By hypothesis, if you only live at night and sleep during the day for 40 years, perhaps your biology could undergo some slight modification and increase your retinal sensitivity.
But that's not the case for you and not even with Jon (and others).   

 

 

Henry 

Edited by ECP M42, 12 December 2021 - 01:22 AM.

[ECP M42]

For Bishop, the ratio of 6x25 performance to 10x25 performance is 150/250, and the relative performance of my 8x32EL to Henry’s 10x25 is 256/250. The ratio of 10x25 to 10x50 is 250/500. How does your binocular observing experience compare to Bishop’s simplified mathematical model? 

Without going into the more complex details of mathematics and science, as we can all see, there are various "indices of merit" to calculate the function of binoculars in a simplified way.
One is the one you mentioned, but there is also the crepuscular index (by A. Kuehl - taken up in 1957 by H. Koehler and R. Leinhos, of Zeiss), the index of A. Adler, the index of C. Fankhauser and an index for the brightest twilight (civil and half of nautical). 

 

Now, each of these index uses the magnification and aperture data (this to simplify), because when the magnification value is also present, the aperture data "automatically" becomes the exit pupil data (which is what it takes).

So, we remember always the exit pupil is the only luminous data of the binoculars (even in these cases). 

 

But what often escapes most users is that each index can only classify binoculars for a specific task or a narrow luminance range. For example, twilight index of Zeiss is only useful for the luminance conditions of astronomical twilight. But most likely, due to the difference in individual retinal sensitivity, each of us could consider one index more appropriate than another, in similar situations. 

 

The Adler index, seems to work more for night stellar observation. And doing two simple calculations, the results of the 3 binoculars you mentioned become:

8√32 = 45, 10√25 = 50 and 10√50 = 70. 

 

I don't know if one or the other index is more correct or not for looking at the stars, but simply based on the individual and the situations (sky, objects, quality of the binoculars, etc.), it could be more or less congruent. 

 

 

[gwlee]

Henry,

 

In post #272, you wrote: “As I have already explained, for my eyes and especially under my polluted skies, the difference between 10x25 and 10x50 is practically invisible.”  In post #260, Fiske included two computer simulations of Melotte 20 that show the expected views from 10x25 and 10x50 binoculars. 

 

How do each of the simulations compare to what you actually see in your 10x25 and 10x50 binoculars?

 

Gary

[ECP M42]

Gary, Fiske's simulation simply collects two different magnitude limits and therefore a different visualization of the quantity of stars, in an equally black sky.
That simulation is completely incongruous, in general and especially with what I see in my sky. But I'm sure it's incongruent for Fiske's (and others) sky too.